Shield for spark plugs



Sept 1942- H. RABEZZANA 2,296,054

SHIELD FOR SPARK PLUGS Filed June 20, 1929 Patented Sept. 15, 19422,296,054

. covered by a metal sheath l9.

.umTEo STATES PATENT OFFICE suntan roa sranx rwos Hector Babeuana,Flint, Micln, assignor, by

mesne assignments, to General Motors Corporation, Detroit, Micln, acorporation of Delaware Application June 20, 1929, Serial No. 372,438

lclaims. (Cl. 123-169) This invention relates to an ignition device andis designed especially to shield a spark plug for use with an internalcombustion engine. One primary object or the invention is to preventinterference with the reception of radio waves by receiving sets used onmotor vehicles, aeroplanes or the like. Another and related object is toaccomplish the primary object by shielding the spark plug used with theengine of such vehicles. Such shielding of the spark plug may, withinthe scope oi this invention, be associated with a shielding of the cableto the plug as shown and described in my Patent #1,69'l,822.

It is found that when radio receiving sets are carried by aeroplanes andmotor vehicles equipped with internal combustion engines, thatunshielded leads to the spark plugs and the unshielded electrodes in theinsulators oi the spark plugs radiate energy, to such an extent as tointerfere with the reception oi! the radio waves by the receiving sets.In my prior patent provision was made for shielding the cables to theplugs. In the present case provision is made to shield the electrodewithin the plug and the latter device is to be associated with theshielded cable by utilizing a common ground connection,

preferably by electrically uniting the metal sheath of the cable withthat of the plug and grounding the latter to the metal shell of theplug.

In the drawing illustrating an embodiment of the invention th figure isa view in elevation of a plug and its lead shielded to accomplish theobject set forth.

Referring to the drawing by reference characters, numeral 3 represents aspark plug having a shell 5, threaded at its lower end as at I, to bemounted in an opening in the cylinder block, not shown. The spark plugshell is provided with a terminal 9 and an electrode ll, insulated fromthe metal shell. The electrode il extends from a position adjacent theterminal 9, up through the plug to a point l2, where it is to be placedin electrical contact with the extremity of a suitable high tension wireiii. The spark plug is covered by a cap 2!, preferably of Bakelite.Within the cup is screwed a ring 22, to which is secured one end ofspring 24. The spring engages the end l2 oi the electrode and also theend of the high tension lead l3, when the parts are assembled. The hightension lead is to be covered by suitable insulation, represented bynumeral l1, and the latter is to be The spark plug cap 2| is plated witha copper coating 23 or otherwise covered by a metallic surface. Such 55sion lead wire, means for electrically connecting a metallic surface maybe provided in the act of molding the Bakelite cap or it may be placedover the cap after its manufacture. As shown at 25, the sheath of thewire it is in metal-tometal contact with an extended end of the metalcover 23 of the Bakelite cap. Hinge clamps 21 are shown as pivoted at 29to the cap. Springs 3! seated against internal projections 33 of theclamps and against external projections 35 of the cap are operative topress the ends of the clamp 31 against the hexagonal portion 39 of theplug, and thereby to hold the ends of the plated surface ll firmlyagainst the grounded metal shell 5 or the plug. As a result of thisconstruction, the electrode extending through the plug is completelyshielded by the plated or metal surface surrounding the Bakelite cap andthe electrode is so protected that it is incapable of radiating energyin a way to interfere with the reception of radio waves by the receivingset. When, as shown in the drawing, this expedient is associated withthe shielding oi! the high tension leads to the spark plugs, asubstantially complete avoidance of interference is attained.

The device is readily assembled by placing the cap over the spark plug,the end of the electric wire. i3 making contact with the electrode as atl2 through the instrumentality oi the spring 24, in the act of assembly.The parts are then secured to the plug by the use or the clamps 21. Theclamps 21 not only hold the cap on the plug but also by the engagementof sheath 23 with the metal surface oi. the plug, insure the ground- 1.In combination with a spark plug, having a metal shell, an insulatingcover for said plug, a metallic sheath encompassing said cover, andmeans structurally independent of the plug for engaging the same tothereby detachably hold said insulating cover thereupon, and to groundsaid metallic sheath upon th metal shell of the plug, so that the covermay be removed without disorganizing the plug.

2. The invention defined by claim 1 together with a lead connected tosaid plug, said lead having a metallic sheath in electrical contact witthe sheath of the plug.

3. In a detachable shield construction for a spark plug employing arubber covered high-ten- 2 said lead wire to the plug terminal, anelectrically continuous metallic covering extending from the metal baseor the plug over its exterior and over the outside of said high-tensionlead wire, an insulating member within said covering surrounding thespark plug terminal and upper portion of said spark plug insulator forsupporting said high-tension lead wire and for spacing said metalliccovering away from the rubber at the end portion where the rubber tendsto become hot in service, and which insulator is" spaced apart from saidspark plug terminal and from the upper part of said spark pluginsulator, and

means for detachably securing said shield to the spark plug with whichit is used.

HECTOR RABEZZANA.

